Variable magnetic strength permanent magnetic drum



Aug. 2s, 1964 F. S. GREENWALD VARABLE MAGNETIC STRENGTH PERMANENT MAGNETIC DRUM Filed May 12, 1961 2 Sheets-Sheet l Aug. 25, 1964 F. s. GREENWALD 3,146,191

VARIABLE MAGNETIC STRENGTH PERMANENT MAGNETIC DRUM Filed May l2, u1-961 l 2 Sheets-Sheet 2 I N VEN TOR. frfl'aW/L maffia/fl M @I a Bw TTORNE YS United States Patent O 3,146,191 VARIABLE MAGNETIC STRENGTH PERMANENT MAGNETIC DRUM Frank S. Greenwald, Ogden Dunes, Ind., assignor to Indiana GeneralCorporation, Valparaiso, Ind.,-a corporation of Indiana n Filed May 12, 1961, Ser. No.`109,753 11 Claims. V(Cl.`209-223) This invention relates Ato a means for adjusting the magneticifeld of magnetic separators and particularly relates to means for adjusting the useful magnetic .field strength of a permanent magnet separator by adjusting the reluctance of 'a leakage path for magnetic u'x emanating from the permanent magnet assembly of the separator.

The invention is particularly applicable to varying the magnetic 4field strength of permanent magnetic drums as used for .either wet or dry type magnetic separations. Control of the magnetic field strength in many situations enables selective separation of materials of varying magnetic responsiveness and the production of either magnetic or Anon-magnetic products of greater purities.

The Vpresent invention is particularly concerned with an improvement over the magnetic field adjustment means f a vcopending application Serial No. 786,873, filed January 14, 1959, now U.S, Patent No. 2,992,737, issued July 18, 1961, and assigned to the same assignee as the present invention.

The present invention provides a permanent magnet separator wherein a series of vanes of magnetic material are disposed at least partially interiorly of the permanent magnet assembly to provide interior shunt paths between 'the poles of the permanent magnet assembly. The vanes are mounted so as to present a different volume of shunting magnetic material between successive poles Lof the permanent magnet assembly in different positions of the vanes.

It is found that the present structure has a Vtwo-fold advantage over the structure of said copending application. In the first place the vanes -provide more complete shunting than can be obtained with a shunt exterior -to the permanent `magnet assembly as in the copending application. One embodiment of the present invention Was found to give 50% more variation from the maximum to the minimum magnetic field strength yas compared to a comparable device in accordance with the prior copending application. Mechanical refinements can be made which will permit an even greater variation. Secondly, it is possible to use a maximum dimen- Sion in the radial direction for the permanent magnet units and this is not possible in the structure of the copending application without a sacrifice of effective shunting action. Thus, with an exterior shunt, the greater the amount of exposure of vpole surface to the shunt, the more effective the shunting action. On Vthe other hand, the exposure o-f the poles at the interior of vthe drum reduces the space between'the poles which is available for permanent magnet material. It is therefore an important object of the present invention to provide an improved mechanical means for 'varying the magnetic field strength in a permanent magnet separator.

A 'further object of the invention is to provide means for adjusting the working field strength of a permanent magnet separator which provides a greater range of variation of magnetic field strength than prior devices.

Still another object of the present invention is to provide a permanent magnet separator having means for adjusting the working field strength thereof which provides'the required range of yadjustment and yet affords a substantially ,greater effective volume of permanent 3,146,191 Patented Aug. 25, 1964 magnet material to provide a substantially higher maximum work-ing field strength.

Other objects, features and advantages of the present invention will be apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE l isa longitudinal sectional view of a magnetic separator drum having a permanent magnet working field adjustment means in accordance with the present invention; 'and Y FIG. 2 is a fragmentary cross sectional view of the structure of FIGURE 1.

As shown on the drawings:

A permanent magnetic separator for Wet type separations may have a slurry feed introduced to the separator by means of suitable piping for flow under a submerged lower portion of a separator drum such-as indicated at 11 in FIGURE 2, the material to be separated flowing generally in the direction indicated by the arrow 12 in FIGURE 2 into proximity to the lower portion of the drum adjacent the permanent magnet assembly indicated generally by the reference numeral 13. The magnetic solids are attracted to the rotating drum surface by means of the permanent magnet assembly 13 and carried through a series of magnetic fields of successively opposite polarity associated with the permanent magnet assembly to final magnetic discharge as indicated by the arrow 15 in FIGURE 2. The non-magnetic solids with the bulk of the water are carried to a Vtailing discharge as indicated diagrammatically by arrow 16 in FIGURE k2. An operating water level may be maintained in the separating zone as indicated diagrammatically by the dash line 18, for example, with the excess water being carried off through an overiiow discharge as indicated by the arrow 20.

As is well known in the art, suitable means may be provided for confining the flow of the slurry feed introduced as indicated at 12 in FIGURE 2 to a region in close proximity to the drum periphery adjacent poles 90, 91 and 92. The overliow indicated at 20 maybe provided by a vertical wall whose top horizontal edge is at the level indicated at 18 in FIGURE 2 to prevent the liquid level from rising above this level. Suitable means is, -of course, provided for collecting the concentrate which is carried by the drum above the water level for discharge by gravity or other suitable means generally as indicated by the arrow 15.

Referring to FIGURE l, it will be observed that the drum 11 may comprise a cylindrical shell or material conveyor 30 having an exterior surface for receiving and conveying magnetic material to be separated. The Vshell 30 is secured to annular rings 34-and 35 which in turn have end plates 36 and 37 secured thereto by means of screws such as shown at 38. The end plates 36 and 37 are journalled on stub shafts 40 and 41 by means of bearings such as indicated at 43 vand 44. The bearings are retained on the shaft by means of caps 47 and 48 secured to the end plates 36 and 37 by means of screws such as 50.` Suitable seals are indicated at 53, 54, 55 and 56 for lprotecting the bearings. It will be understood that a sprocket wheel is secured to one of the end plates 36 or 37 for rotating the drum 11 on stub shafts 40 and 41. Fixed supports for the stub shafts '40 and 41 are indicated diagrammatically at 60 and 61.

The fixed permanent magnet assembly designated generally by the reference numeral 13 may comprise support plates 70 and 71 of non-magnetic material secured by means of hubs 73 and 74 in fixed relation on therstub shafts 40 land 41. Suitable means may be provided externally of the drum 11 for adjusting the angular position ofthe stub shafts 40 and 41 to adjust the angular position 3 of the magnet assembly. In operation of the separator, the stub shafts 40 and 41 are fixed in a predetermined angular position to maintain a predetermined fixed position of the magnet assembly 13.

Extending between the support plates 70 and 71 are a series of flat holding plates of non-magnetic material 80, 81, 82, 83 and 84. The lower margins of the support plates 70 and 71 such as margin 85 of plate 70 seen in FIGURE 2 may be of arcuate configuration and define segments of a circular arc about the axis of shafts 40 and 41 so as to be concentric with the interior surface of the shell 30 and spaced from the interior surface substantially only the distance necessary to provide a clearance gap accommodating rotation of the shell 30 relative to the magnet assembly. The support plates 70 and 71 may be notched as indicated at 85a and 86a in FIGURE 1 to receive successive pole piece strips 90-95. The ends of the strips are secured to the support plates 70 and 71 by any suitable means. The holding plates 80-84 may be suitably secured to the lower surfaces of the permanent magnet wafers 130.

The pole structures of the permanent magnet assembly further comprise pole piece members 100-105 which as seen in FIGURE l are elongated axially of the drum but terminate in spaced relation to the supporting plates 70 and 71. Suitable spacer pieces such as indicated at 107 and 108 of non-magnetic material may be interposed between the opposite axial ends of the pole members 100- 105 and the support plates 70 and 71. It will be observed that the lower margins of the pole strips 90-95 are substantially as close to the inner peripheral surface of the shell 30 as possible while still providing the necessary clearance gap.

In the illustrated embodiment, the permanent magnet assembly further comprises stacks of permanent magnet units such as indicated at 130 of uniform dimensions. In the illustrated embodiments, the permanent magnets are arranged in two layers in the radial direction and six rows 110-115, FIGURE 1, in the circumferential direction. Cover plates are indicated at 131, 132, 133, 134 and 135 in FIGURE 2 for row 111 of the permanent magnets. The cover plates may be secured to the upper surfaces of the stacks of permanent magnet units in any desired manner.

l In the illustrated embodiment each of the permanent magnet units 130 of a given stack is magnetized in the same direction through the thickness dimension of the permanent magnet unit so as to provide directions of magnetization as indicated by arrows 150-154 and 160-164 in row 111, for example. Rows 110 and 112-115 may provide stacks of permanent magnet units magnetized in the same direction as indicated for the axially aligned stacks of row 111 in FIGURE 2. With these directions of magnetization, pole strips 90, 92 and 94 may be considered of south magnetic polarity throughout their axial extent, while pole pieces 91, 93 and 95 may be considered of north magnetic polarity.V Material carried along by the exterior surface of the shell during rotation of the drum thus experiences successively a south pole at 90, a north pole at 91, a south pole at 92, a north pole at 93, a south pole at 94 and a north pole at 95, after which the magnetic material is no longer attracted to the drum surface and is discharged as indicated by the arrow in FIGURE 2.

It is found highly advantageous to utilize ceramic permanent magnet material for the units 130 such as known by the trademarks Indox V. The utilization of permanent magnet material for the energization source of the magnet assembly is, of course, a distinctive advantage as compared to electromagnetic energization, since no source of electrical energy exterior to the drum is then required. The utilization of Indox V ceramic permanent magnets yprovides an improved energy source, enabling utilization of the total magnetic energy much more efficiently than prior art structures. The Indox V ceramic permanent l magnet units can be suitably made into one specific standard shape enabling the use of multiple members of this one shape in various arrangements to efficiently construct magnetic separators of different Widths, of different diameter and of different magnetic intensities and field distributions.

In accordance with the present invention each pole piece member 1011- is provided with a series of notches such as indicated at 102a, 102b and 102C in FIGURE 1. As seen in FIGURE 2, the notches of the successive pole pieces such as indicated at 100a-105a may advantageously be of the same radial depth so as to receive a series of vanes 170a, 170b and 170C, FIG- URE 1, of a shunting member 170 of magnetic material. As seen in FIGURE 2, the axially elongated body portion 170d of the shunting member 170 may be of generally semi-circular configuration so as to be concentric with the drum shell 30, while the vanes may have a progressively increasing radial dimension from one circumferential end thereof to the other so as to provide a volume of magnetic material within the permanent magnet assembly dependent upon the angular position of the shunting member 170. It will be observed from FIG- URE 1, that rows and 111, rows 112 and 113, and rows 114 and 115 of the permanent magnet stacks are spaced apart a distance somewhat greater than the axial dimension of the notches such as 102a-102c so as to freely receive the vane elements a-170c therein.

As best seen in FIGURE 1, the shunting member 170 may be mounted on a shaft 171 carried within the stub shafts 40 and 41 by means of bearings 173, 174 and 175. The shunting member 170 is supported from the shaft 171 by means of support plates 176 and 177 secured t0 the shaft 171 by means of collars 180 and 181. Keys 183 and 184 extend into cooperating keyways in the collars and in the shaft 171. Set screws are indicated at and 191 for retaining the parts in the desired positions. An adjusting handle may be provided at the outer end of shaft 171 exterior of the drum 11 for adjusting the angular position of the shunting member 170 relative to the permanent magnet assembly 13.

In operationr of the embodiment of FIGURES 1 and 2, the drum 11 is rotated in the clockwise direction `as indicated by arrow 197 in FIGURE 2 and material is fed beneath the first pole 90. Magnetic material is lifted to the rotating shell 30 of non-magnetic material and transported from pole to pole for ultimate discharge upon leaving the influence of the last magnetic pole strip 95. Experience has shown that the greatest control of quality of magnetic separation occurs in the initial magnetic pickup zone or through the area of the first three magnetic poles 90, 91 and 92. This, therefore, is the zone in which the maximum control of magnetic field strength exterior to the drum is desired. The last three poles 93, 94 and 9S are used for transportation of the magnetic material to eventual discharge, so that it is desired to have less reduction of field strength at these last three discharge poles. The configuration of the shunting vanes 170a-170c as shown in FIGURE 2 provides the maximum variable control in the intial pick-up zone at poles 90-92. The leakage flux paths provided by the vanes between the successive poles are largely interior of the permanent magnet assembly and, of course, extend generally circumferentially along the vanes between the successive poles. It will be observed that the volume of magnetic material provided by the vanes which is within the permanent magnet assembly 13 may be substantially continuously Varied over a relatively wide range by adjusting the angular position of the shunting assembly 170 through rotation of handle 195, FIGURE 1, at the exterior of the drum 11. The solid line position of the shunting assembly 170 in FIGURE 2 illustrates the angular position of the shunting assembly for minimum working magnetic field strength at the exterior of the' drum, while the position of the assembly shown in dot dash outline at 170 in FIGURE 2 provides maximum effective magnetic field strength at the exterior of the drum. As indicated in FIGURE 2, the vanes 170a- 170e which may, for example, be of mild steel, preferably have a radial extent at the maximum radius portion thereof to extend into substantially more than 50% of the radial extent of the permanent magnet assembly 13.

It is found that the use of shunting means such as vanes 17.0a-170c which extend into the interior of the permanent magnet assembly has a two-fold advantage. In the first place the vanes provide more complete shunting at a given angular position than can be obtained with a comparable shunt entirely external of the permanent magnet assembly. At the same time, it is possible to use amaximum dimension for the permanent magnet stacks in the radial direction. In order to explain the latter advantage it should be understood that for a permanent magnet arrangement such as shown in FIGURE 2 having a given length of the permanent magnet stack in its direction of magnetization, there is a maximum radial dimension for the permanent magnet in a `drum separator having a given outside diameter. Such maximum dimension is illustrated in FIGURE 2 where the adjacent stacks of permanent magnet units touch each other at their radial innermost extremities as indicated at 200 for example. In order to get the maximum field strength it is necessary to employ the maximum amount of permanent magnet material in each stack. The device of the present invention permits this condition. On the other hand, where the -shunting device is entirely external of the permanent magnet assembly, the pole pieces must be exposed at the radial inner side of the permanent magnet assembly to provide the required effectiveness of the shunting member. It wil-l be evident in FIGURE 2 that if the pole members 101, 102, 103 and 104 were required to extend to the radial innermost part of the permanent magnet assembly and have substantial surfaces exposed at the radially inner side of the assembly considerably less permanent magnet material could be utilized for a given drum configuration. With the present invention, the amount of permanent magnet material omitted to provide clearance for the vanes 170ae170c can be compensated by a small increase in the axial length of the permanent magnet assembly.

The superior shunting effectiveness provided by an interior shunt as compared to an exterior shunt has been demonstrated by actual experiment. Two permanent magnet drum-type separators were constructed of comparable dimensions except that one utilized an entirely external shunting device while the other used shunting vanes as shown in the illustrated embodiment of the present invention. It was found that the device in accordance With the present invention provided half again as much variation from the maximum to the minimum magnetic field strength adjustments of the lshunting .assembly. Mechanical refinements can be made which will permit an even greater variation. Both drums compared had the same magnetic structure except for the radial dimension of the permanent magnet stacks and both included the maximum amount of permanent magnet material for which space was available. The device in accordance with the: present invention also gave an approximately greater maximum field strength because of the greater amount of permanent magnet material accommodated by the present configuration.

While the present invention is particularly applicable to a drum type permanent magnet separator, the broad concepts of the present invention may be applied to other permanent magnet devices wherein it is useful to adjust the effective external field of the assembly Vas will be apparent to those skilled in the art from a consideration of the present disclosure'.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim :as my invention:

l. In a permanent magnet separator comprising a rotatable material conveying drum, and a permanent magnet assembly within the drum having a plurality of pole pieces adjacent the interior surface of the drum and having permanent magnets `extending between the pole pieces and magnetized in the direction between `said pole pieces for establishing a working magnetic `field at the exterior of the drum, the improvement comprising shunting means of magnetic material within said drum and disposed at least partially within the confines of the permanent vmagnets themselves in the region between the pole pieces which `region is offset from ythe pole pieces in the direction of magnetization of the permanent magnets; and movable relative to said pole pieces to a plurality of ,shunting positions providing successively greater volumes of magnetic material within the contines of .the permanent magnets themselves in said region between the pole pieces at the interior of said permanent magnet assembly, and means for moving said yshunting means selectively relative to said pole pieces to `said shunting positions to correspondingly adjust the strength of the working magnetic field exterior to said drum.

2. vA drum type permanent magnet separator .comprising a rotatable drum for conveying material to be separated, a permanent magnet assembly adjacent the interior surface of said drum comprising a series of axially elongated pole pieces Aspaced arcuately within the drum and lhaving circumferentially aligned notches at the radially inner sides thereof, stacks of permanent magnet units extending between Said pole pieces at each axial side of said notches and providing spaces there.- between in circumferential alignment with said notches, and vane means of magnetic material in circumferential alignment with said notches in said pole pieces and movable in said notches and in the spaces between said stacks of permanent magnet units Valigned therewith to provide shunting magnetic flux paths between said pole pieces interiorly of said permanent magnet assembly.

3. In a permanent magnet separator comprising a per.- manent magnet assembly having la plurality of magnetic pole pieces with magnets interposed between said pole pieces and magnetized in the direction 'between said pole pieces to produce a working magnetic field exterior to said permanent magnet assembly at one side thereof, and means for conveying material to be separated through said working magnetic field at said one side of ,said permanent magnet assembly, the improvement lof a working magnetic field adjustment device including magnetizable material located at least partially vwithin the conf fines of the permanent magnets themselves in the region between the pole pieces at the interior of said permanent magnet assembly which region is offset from the pole pieces in the direction of magnetization of the permanent magnets and defining a shunt pathfbetween said pole pieces extending through said region between the pole pieces, and means for adjusting the volume of said magnetic material within the confines of the permanent magnets themselves in said region between the pole rpieces at the interior of said ypermanent magnet assembly by movement of the magnetic material relative to said pole pieces to correspondingly adjust the Vstrength of said working magnetic field and providing for at least one position of said device in which said magnetizable material in said region between the pole pieces extends at least for a substantial portion of the distance between said pole pieces.

4. A permanent magnet separator comprising a -rotatable material conveying drum, a permanent magnet assembly within the drum having a plurality of pole pieces adjacent the interior surface of the drum and having permanent magnets extending between the pole pieces for establishing a working magnetic field at the exterior of the drum, said permanent magnet assembly having a Vseries of channels extending `therethrough at the radially inner side of the assembly, and shunting means of magnetic material within said drum and movable in said channels to a plurality of shunting positions providing successively greater volumes of magnetic material within the coniines of said permanent magnet assembly, and means for moving said shunting means selectively to said shunting positions to correspondingly adjust the strength of the Working magnetic lield exterior to said drum.

5. A drum type magnetic separator comprising a rotatable drum for conveying material tot be separated, a permanent magnet assembly adjacent the interior surface of said drum comprising a plurality of axially elongated pole pieces spaced apart in the circumferential direction within the drum, and stacks of ceramic permanent magnet units extending between said pole pieces and spaced axially apart to define at least one circumferentially directed channel between said pole pieces, shunting means of magnetic material in alignment with said channel between said stacks of ceramic permanent magnet units and movable into a succession of shunting positions in said channel providing successively greater volumes of magnetic material within said channel, and means providing for movement of said shunting means selectively to said shunting positions to correspondingly adjust the strength of the working magnetic eld exterior to said drum.

6. In combination with a permanent magnet device comprising a permanent magnet assembly having a plurality of magnetic pole pieces with permanent magnets disposed between said pole pieces and magnetized in the direction between said pole pieces to produce a working magnetic eld between said pole pieces and exterior to said permanent magnet assembly at one side thereof, the improvement of a working magnetic iield adjustment device including magnetizable material located at least partially within the contines of the permanent magnets themselves ina region between the pole pieces at the interior of said permanent magnet assembly which region is offset from the pole pieces in the direction of magnetization of the permanent magnets and dening a shunt path between said pole pieces, and means for adjusting the position of said magnetizable material within the confines of the permanent magnets themselves in said region between the pole pieces of said permanent magnet assembly by movement of the magnetizable material relative to said pole pieces to adjust the strength of said working magnetic lield and providing for at least one position of said device in which said magnetizable material in said region extends at least for a substantial portion of the distance between said pole pieces.

7. In a permanent magnet separator comprising a rotatable material conveying drum, and a permanent magnet assembly within the drum having a plurality of pole pieces adjacent the interior surface of the drum and having permanent magnets disposed adjacent the interior surface of the drum` and extending between the pole pieces and magnetized in the direction between said pole pieces for establishing a Working magnetic iield at the exterior of the drum, said pole pieces engaging opposite end faces of said permanent magnets with respect to the direction of magnetization of the permanent magnets and the working magnetic iield extending across a radially outer side of the permanent magnets, the radially outer side of the permanent magnets being disposed generally at a irst radial distance from the axis of the drum, the permanent magnets having a radially inner side extending generally at a second radial distance from the axis of the drum and the permanent magnets having respective side faces extending generally parallel to the direction of magnetization thereof and extending generally radially between the radially outer and the radially inner sides of the permanent magnets, the improvement comprising shunting means of magnetic material within said drum and elongated in the direction of magnetization of said permanent magnets and disposed in ,radially overlapping relationship to said permanent magnets and in the region directly adjacent at least one of said side faces of said permanent magnets which region is located between said first radial distance and said second radial distance from the axis of said drum and movable to a plurality of shunting positions in said region having successively greater shunting eifect with respect to the strength of the working magnetic ield including a position wherein said magnetic material extends in said region for at least a substantial proportion of the distance between said pole pieces, and means for moving said shunting means selectively to said shunting positions to correspondingly adjust the strength of the working magnetic eld between said pole pieces exterior to said drum.

8. In a permanent magnet separator comprising a permanent magnet assembly having a plurality of magnetic pole pieces and having permanent magnets interposed between said pole pieces adjacent one side of said permanent magnet assembly and magnetized in a direction between said pole pieces to produce a working magnetic iield exterior to said permanent magnet assembly at said one side thereof and at one side of the permanent magnets, said pole pieces confronting opposite end faces of said permanent magnets with respect to the direction of magnetization of the permanent magnets, the permanent magnets having an opposite side opposite said one side and having respective side faces extending generally parallel to the direction of magnetization and extending between the one side and said opposite side of said permanent magnets, and means for conveying material to be separated through said working magnetic eld at said one side of said permanent magnet assembly, the improvement of a working magnetic eld adjustment device including magnetizable material located at 4least partially in` laterally overlapping relationship to said permanent magnets with respect to a direction toward said one side of said permanent magnet assembly from the opposite side thereof and in a region directly adjacent one of said side faces of said permanent magnets which region is located between'said one side and said opposite side of said permanent magnets and defining a shunt path between said pole pieces in said region, and means for adjusting the volume of said magnetic material which is in laterally overlapping relationship to said permanent magnets in said region to correspondingly adjust the strength of said working magnetic field between said pole pieces.

9. In a permanent magnet device comprising a permanent magnet assembly for producing a working magnetic iield at a region exterior thereto, said assembly comprising a group of permanent magnets occupying a volume adjacent said working magnetic iield region and magnetized in directions of magentization to produce said working magnetic eld, the improvement comprising said group of permanent magnets having channels extending therein and within said volume occupied by said permanent magnets so as to provide magnetic flux paths within said volume for magnetic flux from said permanent magnets, magnetic material in said channels, and means adjustably mounting said magnetic material for selective movement to any of a plurality of positions with respect to said channels providing respective different volumes of said magnetic material within said channels.

10. The device of claim 9 with certain of said magnets of said group being spaced apart transversely of their directions of magnetization by a distance substantially less than the transverse dimensions of said magnets to define said channels, and said channels extending generally parallel to the directions of magnetization of the magnets adjacent said channels and providing leakage magnetic ilux paths for magnetic flux emanating from the adjacent magnets, whereby adjustment of the volume of magnetic material in said channels adjusts the strength of the working magnetic eld of the permanent magnet assembly.

11. In a permanent magnet separator comprising a permanent magnet assembly having a plurality of magnetic pole pieces with magnets interposed between said pole pieces to produce a Working magnetic field exterior to said permanent magnet assembly at one side thereof, and means for conveying material to be separated through said working magnetic field at said one side of said permanent magnet assembly, the improvement of a working magnetic ield adjustment device including magnetizable material located at least partially within the interior of said permanent magnet assembly and defining a shunt path between said pole pieces, and means for adjusting the volume of said magnetic material at the interior` of said permanent magnet assembly by movement of the magnetic material relative to said pole pieces to correspondingly adjust the strength of said working magnetic iield, said pole pieces extending transverse to the direction of movement of said conveyor means so that the material conveyed thereby travels past magnetic poles of successively different polarity, and said magnetizable material being elongated in the direction of movement of said conveying means and extending across a plurality of said pole pieces, said magnetizable material extending through a plurality of said pole pieces transversely thereto, and said pole pieces having a series of aligned notches therein aligned with respect to the direction of movement of said conveying means, and said magnetizable material extending through said aligned notches and being movable therein relative to said pole pieces.

References Cited in the le of this patent UNITED STATES PATENTS 1,324,529 Ullrich Dec. 9, 1919 2,179,305 Stickney Nov. 7, 1939 2,785,801 Laurila Mar. 19, 1957 2,873,413 Reyvst Feb. 10, 1959 2,945,590 Stearns July 19, 1960 2,992,737 Buus July 18, 1961 FOREIGN PATENTS 461,816 Great Britain Feb. 25, 1937 

1. IN A PERMANENT MAGNET SEPARATOR COMPRISING A ROTATABLE MATERIAL CONVEYING DRUM, ANDA PERMANENT MAGNET ASSEMBLY WITH THE DRUM HAVING A PLURALITY OF POLE PIECES ADJACENT THE INTERIOR SURFACE OF THE DRUM AND HAVING PERMANENT MAGNETS EXTENDING BETWEEN THE POLE PIECES AND MAGNETIZED IN THE DIRECTION BETWEEN SAID POLE PIECES FOR ESTABLISHING A WORKING MAGNETIC FIELD AT THE EXTERIOR OF THE DRUM, THE IMPROVEMENT COMPRISING SHUNTING MEANS OF MAGNETIC MATERIAL WITHIN SAID DRUM AND DISPOSED AT LEAST PARTIALLY WITHIN THE CONFINES OF THE PERMANENT MAGNETS THEMSELVES IN THE REGION BETWEEN THE POLE PIECES WHICH REGION IS OFFSET FROM THE POLE PIECES IN THE DIRECTION OF MAGNETIZATION OF THE PERMANENT MAGNETS; AND MOVABLE RELATIVE TO SAID POLE PICES TO A PLURALITY OF SHUNTING POSITIONS PROVIDING SUCCESSIVELY GREATER VOLUMES OF MAGNETIC MATERIAL WITHIN THE CONFINES OF THE PERMANENT MAGNETS THEMSELVES IN SAID REGION BETWEEN THE POLE PIECES AT THE INTERIOR OF SAID PERMANENT MAGNET ASSEMBLY, AND MEANS FOR MOVING SAID SHUTING MEANS SELECTIVELY RELATIVE TO SAID POLE PIECES TO SAID SHUNTING POSITIONS TO CORRESPONDINGLY ADJUST THE STRENGTH OF THE WORKING MAGNETIC FIELD EXTERIOR TO SAID DRUM. 